The invention concerns a method of providing impedance matching between a line impedance Z.sub.line with two transmission terminals, and a transmitter/receiver unit connected thereto as well as an interface unit for providing such an impedance matching.
Historically, public service telephone networks (PSTN) have developed as isolated networks with individual specifications--including network impedance. These networks are now used widely, and it is not readily possible to change the specifications of a network without affecting the operation for the users of the network. This means in practice that a new type of telephone apparatus to be marketed e.g. all over Europe must be designed in a large number of versions with different network interfaces corresponding to the number of different network impedances. This involves problems of logistics for the manufacturers of signalling devices, since devices for one market cannot readily for used on another market.